Aqueous concentrate formulations of pesticidal and plant growth modifying chemicals are widely used in agricultural, industrial, recreational and residential areas worldwide. The chemicals which form the active ingredients of such formulations illustratively include insecticides, fungicides, herbicides, plant growth regulators and plant nutrients. An aqueous concentrate is essentially a solution of the active ingredient in water at relatively high concentration, intended for dilution in water prior to application by spraying or other means. Typically the aqueous concentrate is diluted in about 10 to about 100 times its own volume of water prior to application.
If the active ingredient is to be applied to the foliage of plants, a surfactant is typically included in the formulation to aid wetting of the foliage by the spray solution and improve retention and uptake of the active ingredient by the plant. Because the spray solution must contain a sufficient concentration of said surfactant to provide good wetting, retention and uptake, and therefore good efficacy, the aqueous concentrate formulation must generally contain a high concentration of the surfactant, typically about 5% to about 25% by weight of the formulation.
A common concern with many surfactants that provide good efficacy of the active ingredient is that at the high concentrations required in the aqueous concentrate formulation the surfactants tend to be irritant if accidentally splashed or otherwise injected into the eye of anyone handling such a formulation. This property may lead to restrictive labelling of the product that limits its usefulness in certain markets, even where the active ingredient itself provides no such hazard.
A class of surfactants that are known to give excellent efficacy of certain foliar-applied pesticides and plant growth modifying agents, but are irritant to eyes at the high concentrations required in aqueous concentrate formulations, are alkoxylated alkylamines. These are especially widely used in aqueous concentrate formulations of the herbicide N-phosphonomethylglycine, commonly known as glyphosate.
Glyphosate is a highly effective and commercially important herbicide useful for combating the presence of a wide variety of unwanted vegetation, including agricultural weeds. Glyphosate is applied as a formulated product to the foliage of annual and perennial grasses, sedges and broadleaf plants and the like, and is taken up over a period of time through the leaves into the treated vegetation, whence it translocates throughout the plant.
Glyphosate in its acid form has relatively low water solubility, but when formulated as a salt its solubility is much higher. Aqueous concentrate formulations of glyphosate therefore typically contain one or more salts, such as an alkylamine, for example, isopropylammonium, salt, the ammonium salt, the trimethylsulfonium salt or an alkali metal, for example potassium or sodium, salt of glyphosate.
A wide variety of alkoxylated alkylamine surfactants have been tested or used commercially in glyphosate formulations. They may be represented generically by the structural formula ##STR1## wherein R.sub.1 is C.sub.8-22 alkyl, R.sub.2 groups are C.sub.2-4 alkylene groups or a mixture of such groups and m and n are numbers such that m+n has an average value in the range from about 2 to about 50. In commercial formulations R.sub.1 is most commonly derived from a natural source such as tallow, soybean or coconut oil and comprises a range of chain lengths, and R.sub.2 is most commonly ethylene.
Aqueous concentrate formulations of the isopropylamine salt of glyphosate with a surfactant based on ethoxylated tallowamine have been sold by Monsanto Company for many years under various trade names including Roundup.RTM. herbicide.
European patent application 0 290 416 discloses aqueous concentrate formulations of glyphosate or its salts with a surfactant having the structure represented above wherein R.sub.1 is C.sub.8-22 alkyl, R.sub.2 is alkylene, for example ethylene or propylene, and m+n has an average value in the range from about 1 to about 12, and wherein the weight ratio of glyphosate (expressed as acid equivalent) to said surfactant is in the range from about 1:1.75 to about 6:1.
Eye irritant properties of alkoxylated alkylamine surfactants are well known, and are disclosed, for example, in Australian patent application 81718/91. This patent application discloses surfactant compositions comprising an alkoxylated alkylamine of the structure represented above wherein m+n has an average value of at least about 7, together with compounds said to reduce the eye irritancy of said alkoxylated alkylamine. The eye irritancy reducing agents disclosed include sulfated polyoxyalkylene alkylphenols, alcohol sulfates, polyoxyalkylene alcohol sulfates, mono- and dialcohol sulfates, mono- and di-(polyoxyalkylene alcohol) phosphates, mono- and di-(polyoxyalkylene alkylphenol) phosphates, polyoxyalkylene alkylphenol carboxylates and polyoxyalkylene carboxylates, said eye irritant reducing compounds having alkyl or alcohol groups with a chain length from about 8 to about 20 carbon atoms and up to about 60 moles of alkylene oxide per mole of the compound. It is further disclosed that said surfactant compositions can be used to prepare pesticidal compositions, particularly herbicidal compositions containing glyphosate.
There are provided herein new and useful storage-stable aqueous concentrate compositions comprising (a) a water-soluble pesticide or plant growth modifying agent, (b) an alkoxylated alkylamine surfactant having the molecular structure represented above in sufficient amount to provide good efficacy of said pesticide or plant growth modifying agent when the composition is applied in diluted form to plant foliage, (c) a C.sub.6-22 saturated or unsaturated alkyl monocarboxylic or dicarboxylic acid or mixture of such acids and (d) water; said compositions being less irritant to eyes than similar compositions lacking only component (c).
Saturated or unsaturated alkyl monocarboxylic or dicarboxylic acids have not previously been disclosed to act as eye irritancy reducing agents when used with eye irritant surfactants, such as alkoxylated alkylamines. They have advantages over the eye irritation reducing agents disclosed in Australian patent application 81718/91 cited above in having lower cost.
U.S. Pat. No. 5,196,044 discloses that fatty acids of carbon chain length from about 7 to about 20 may be used in combination with certain herbicides, including glyphosate based herbicides, to give improved herbicidal performance. Examples are provided wherein nonanoic acid, in the form of an 80% (by weight) formulation called Sharpshooter.RTM. herbicide, was diluted as a spray mix together with the isopropylamine salt of glyphosate, in the form of Roundup.RTM. herbicide. No disclosure is made of an aqueous concentrate formulation comprising a herbicidal active ingredient, an alkoxylated alkylamine surfactant and a saturated or unsaturated fatty acid. No mention is made of eye irritancy properties of any composition disclosed; nor is any guidance given as to how to prepare a storage-stable aqueous concentrate formulation comprising both glyphosate and saturated or unsaturated fatty acid. The spray mixes disclosed contain a sufficient quantity of the fatty acid to provide enhanced weed control performance by comparison with the herbicide alone. For example, the weight/weight ratios of nonanoic acid to glyphosate (expressed as acid equivalent) in disclosed spray mixes ranged from 1:3 to 62:1.
PCT application WO 92/07467 discloses dilute aqueous compositions comprising glyphosate or derivatives or salts thereof together with a fatty acid or fatty acid salt, which are said to provide herbicidal activity at rates lower than those of either component alone required to provide comparable activity. The fatty acid or fatty acid salt component is present in the range from 0.1% to 3.0% by weight of the composition while the glyphosate component is present at 0.08% to 2.0% by weight of the composition. Again, no mention is made of eye irritancy properties of any composition disclosed; nor is any guidance given as to how to prepare a storage-stable aqueous concentrate formulation comprising both glyphosate and fatty acid. All data provided relate to dilute mixtures of Roundup.RTM. herbicide with fatty acid salts as opposed to fatty acids, with the exception of data provided in Table 4 of the cited application. This Table 4 presents data on various dilute mixtures of Roundup herbicide with a 1:1 formulation of soybean and coconut fatty acids. These mixtures, when compared with Roundup herbicide alone, are shown to provide slightly superior herbicidal efficacy on two weed species and inferior herbicidal efficacy on a third weed species.
European patent application 0 566 648 discloses aqueous formulations comprising a salt of glyphosate and at least one fatty acid or salt thereof, wherein the fatty acid or salt thereof is present in an amount sufficient to provide herbicidal activity in its own right, in the form of early contact injury symptoms. An appropriate pH range is disclosed (about 6.4 to about 7.8, preferably about 6.8 to about 7.0) wherein said formulations are said to show improved storage stability while maintaining the desired herbicidal efficacy. Among surfactants disclosed as optional components of said formulations is an ethoxylated tallowamine surfactant having about 15 to about 18 moles of ethylene oxide per mole of tallowamine. Once again, no mention is made of eye irritancy properties of any composition disclosed. No hint is present that any advantage might be apparent at fatty acid concentrations far below those providing contact injury symptoms, or at pH levels more typical of commercial aqueous concentrate formulations of glyphosate, such as in the range from about 4.0 to about 6.0.